One well-known naturally occurring organometallic compound is vitamin B12.

**What is Vitamin B12?**
- Vitamin B12 is a water-soluble vitamin that is essential for the proper functioning of the nervous system, brain, and the synthesis of DNA.
- It is a complex molecule that contains a metal atom, cobalt, at its center.

**Structure of Vitamin B12**
- Vitamin B12 has a complex structure that includes a corrin ring, a cobalt atom, and a nucleotide side chain.
- The corrin ring is similar to the porphyrin ring found in heme, which is the molecule that carries oxygen in our blood.
- The cobalt atom sits at the center of the corrin ring and is coordinated to four nitrogen atoms.
- The nucleotide side chain is attached to the corrin ring and serves as a binding site for the vitamin in enzymes and proteins.

**Functions of Vitamin B12**
- Vitamin B12 plays a critical role in the synthesis of DNA, which is the genetic material that controls the function and development of all cells in our bodies.
- It is also involved in the metabolism of amino acids and fatty acids, which are important for the production of energy and the maintenance of healthy cells.
- Vitamin B12 is essential for the proper functioning of the nervous system and brain. It helps to maintain the myelin sheath that surrounds and protects nerve cells, and it is involved in the production of neurotransmitters that are essential for communication between nerve cells.

**Sources of Vitamin B12**
- Vitamin B12 is found naturally in animal products such as meat, fish, and dairy products.
- It can also be obtained from fortified foods such as cereals and nutritional supplements.

In conclusion, vitamin B12 is a well-known naturally occurring organometallic compound that plays a critical role in the functioning of our bodies. Its complex structure and essential functions make it an important molecule for understanding the role of organometallic compounds in biological systems.